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Types of Fasting: Definition, Methods & Benefits

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Over the past few years, the popularity of fasting has greatly increased.  Certain types of fasting such as intermittent fasting and time-restricted eating have become frequently discussed in the mainstream media. 

There are many reasons that people choose to fast, such as weight loss, improving circadian rhythm, a longer and healthier life, or even spiritual benefits. 

However, before trying a fasting schedule, it is important to be aware of the different types of fasting, and what the risks and benefits are. 

What is fasting? 

Fasting means going without food for a certain period of time. One popular method of fasting is intermittent fasting, which involves alternating between periods of abstaining from food and eating normally.

What can I eat while fasting?

Generally only water and zero-calorie beverages such as tea and coffee without sugar or milk are permitted during a fasting period. However, some fasting diets allow low-calorie meals to be consumed, as long as the total calorie intake for the day remains low. 

When you are outside the fasting period, there are generally no restrictions to what you can eat, because intermittent fasting focuses on when you eat rather than what you eat. That said, it is recommended that you avoid high calorie foods and highly processed foods, as these can reduce the benefits of the fast. 

Types of intermittent fasting 

There are various types of methods of intermittent fasting, which have been developed by medical researchers and nutritionists. The ‘best’ type of fasting is not known, as research into the benefits of different types of fasting protocols is ongoing. 

The various types of fasting differ based on the length of the eating window and fasting period, how often the fast is performed, and whether low-calorie meals are allowed on fasting days or not. Several common types of intermittent fasting include: 

  • Time-restricted eating
  • Circadian rhythm fasting
  • Alternate-day fasting
  • 5-day fasting
  • Eat Stop Eat
  • The 5:2 diet

These types of fasting are described in more detail below. 

Time-restricted eating

Time-restricted eating is one of the most popular forms of intermittent fasting, as it is relatively simple and involves following the same eating pattern each day of the week. With time-restricted eating, you choose an eating window of 8-12 hours per day, and then fast for 12-16 hours, each 24-hour period. Two common types of time-restricted eating are listed below:

16/8 method

One popular method of time-restricted eating is the 16/8 method, in which you eat all of your calories within an 8-hour window, and then fast for 16 hours. For example, you could eat your first meal of the day at 10 a.m., and finish your last meal by 6 p.m. each day. Alternatively, you could skip breakfast and eat your first meal at 12 p.m., and your last meal by 8 p.m.. 

Overnight method

A simpler type of time-restricted eating is overnight fasting, in which you only fast for 12 hours each 24-hour period. For example, you could eat breakfast at 7 a.m., then finish eating dinner by 7 p.m.. Although the benefits may be less than a 16-hour fast, a 12-hour fast may be easier to maintain in the long term. 

Circadian rhythm fasting

Circadian rhythms refer to the mental and physical changes that occur in your body over a 24-hour period. Circadian rhythm fasting was popularized by Dr Satchin Panda in his book, The Circadian Code. 

Circadian rhythm fasting is a type of time-restricted eating pattern with a strong emphasis on eating earlier in the day. The idea behind this type of fasting is to align your eating pattern with the daylight and nighttime hours of the day, to ensure your body’s internal clock is synced with the environment.

With circadian rhythm fasting, all of your meals are consumed within a 8-12 hour period during the day. With this eating pattern, your first meal should be consumed at least 1 hour after waking up, and you should finish eating at least 2-3 hours before you plan to sleep. For example, if you wake up at 7 a.m. and sleep at 11 p.m., you would eat your first meal at 8 a.m., and your last meal at 8 p.m..

Researchers propose that circadian rhythm may help to extend the healthy period of lifespan. 

Alternate-day fasting 

Alternate-day fasting was made popular by nutrition Professor Krista Vardy. The method involves doing a low-calorie ‘fast’, in which you eat only 25% of your daily calorie needs, every other day, and eating normally on non-fasting days. 

This fasting method is designed for weight loss, and has been shown to be effective for fat loss across several studies. For example, one study showed that participants lost approximately 5 kg (11 lbs) of body weight over 12 weeks while following alternate-day fasting. Another study in non-obese subjects showed that alternate-day fasting resulted in a 2.5 kg (5.5 lbs) decrease in body weight over 22 days. 

5-Day Fast 

The 5-day fast or fasting mimicking diet is a longer fast that was popularized by the book, The Longevity Diet by Valter Longo from the University of Southern California. The author recommends eating a healthy pesco-vegetarian diet throughout the year, and 4 times per year adopting a 5-day fast.

The 5-day fast may be done as a strict water-only fast, or a low-calorie fast with a total of 1-2 meals per day totaling no more than 800 calories. The idea behind the relatively long fast is that some benefits of fasting may require a fast of at least 48-72 hours.

Eat Stop Eat

Eat Stop Eat is a type of fasting that was popularized by the book, Eat Stop Eat: The Shocking Truth that Makes Weight Loss Simple Again by Brad Pilon, and encourages a flexible approach to fasting during the week. The diet involves fasting for a 24-hour period, once or twice per week, and following a regular eating pattern on other days. The calorie intake on non-fasting days may be slightly higher than usual, to make up for the deficit of the fasts. The author also recommends engaging in a weight-training program to complement the benefits of the fasting diet for fat loss. 

The 5:2 Diet 

This method was popularized by the bestselling book, The FastDiet by Dr Michael Mosley. The weekly diet involves eating normally for 5 days, then restricting food consumption to 500-600 calories for 2 days. The idea is that reducing calories for 2 days per week may be psychologically easier than a daily fasting schedule that lasts the entire week. 

Benefits of intermittent fasting 

There are numerous benefits of intermittent fasting, such as weight loss and improved metabolism. These benefits are listed below: 

1. Weight loss 

One of the most popular reasons for fasting is weight loss. Fasting means abstaining from food consumption, which often puts your body into a caloric deficit. In this state, your body has fewer calories than it requires to maintain its current weight, leading to weight loss as stored fat is metabolized as an energy source.

Several studies have shown that intermittent fasting is associated with weight loss. One study showed that participants who followed a 16/8 time-restricted eating pattern lost more weight than those who followed a consistent meal timing approach. Another study in which participants followed an intermittent fasting schedule similar to the 16/8 method resulted in a 3% reduction in body weight over 8 week. A review of studies showed that intermittent fasting was effective at reducing body weight by between 3-7% over 3-12 weeks. 

One study evaluating the 5:2 diet showed that this diet was associated with more than 5% reduction in body weight in 15% of participants. However, this level of weight loss was roughly the same weight loss as the control group that received standard weight management advice.

Fasting may help with weight loss by reducing feelings of hunger and increasing feelings of satiety (fullness). This means that after the fasting period, you may not eat as many calories as you normally would. 

 

2. Improved metabolic health 

Meal timing has been shown to impact metabolism, that is, the bodily processes that convert food into energy. Studies have shown that fasting may be associated with many benefits to metabolic health, such as:

  • Improved insulin signaling and blood sugar control
  • Enhanced absorption of nutrients from the intestines
  • Increased thermal effect of food (the body uses more energy to break down food)

 

3. Longevity benefits 

Research has shown that restricting total calorie consumption extends the lifespan in several organisms such as worms, mice and flies. However, calorie restriction is difficult for humans to maintain over the long-term long-term. Luckily, intermittent fasting has been shown also extends lifespan in animal models, and is speculated to increase human lifespan, too. 

There are several processes that are improved by intermittent fasting that may lead to improved longevity in humans, such as:

  • Promoting autophagy, a kind of ‘cellular cleaning’ that removes debris from the cells and improves the health of mitochondria in the cells.
  • Improving fat cell metabolism and optimize glucose function, both of which are linked to a longer lifespan
  • Promoting weight loss, which may help to reduce the risk of chronic diseases such as heart disease and type 2 diabetes
  • Reducing blood pressure, thereby reducing the risk of a heart disease
  • Reducing inflammation, which is known to drive the aging process

The above processes are thought to be important factors that impact a person’s biological aging process, and his or her expected healthy lifespan. 

 

Challenges of intermittent fasting 

Intermittent fasting will likely take some adjusting to, as there are a few challenges that many people face when starting an intermittent fasting diet, such as: 

1. Hunger

Perhaps unsurprisingly, you may experience feelings of hunger if you are new to intermittent fasting. Even if you are only fasting for 12 hours, you may go to bed hungry, and have to endure periods of hunger in order to follow the prescribed fasting schedule. Some level of hunger and perhaps frustration are normal when starting an intermittent fasting regime.

Luckily, the hunger feelings often decrease over time. Research suggests that your feelings of hunger may decline once your body has adjusted to the fasting process. One study showed that after 3 weeks of fasting, 93% of people had adapted to the process and no longer experienced the hunger feeling. 

 

2. Mood changes 

If you try intermittent fasting, you may become more cranky and notice your mood is less stable. This is because in addition to increased hunger levels, fasting often results in low blood sugar levels, which can cause symptoms of anxiety and irritability.
In addition, fasting may be associated with side effects such as headaches, sleep disturbances and fatigue which could also affect your mood. However, negative changes in mood may not last, as one study showed that fasting over a 3-week period led to overall improvements in emotional wellbeing.

3. Adherence 

Intermittent fasting requires discipline and planning to adhere to. For some people, sticking to a fasting regime may be fairly easy, whereas for others it may be difficult. If you generally rely on intuition to determine when to eat, you may have to change your relationship with eating in order to follow a fasting schedule. Building an eating schedule that is compatible with your weekly schedule may be a good option to maintain intermittent fasting in the long term. 

Who should avoid fasting? 

If carefully planned and supervised by a medical health practitioner, fasting is generally safe for most people.

However, some groups of people should avoid fasting, as it may negatively impact their overall health, such as:

Conclusion

Fasting involves giving up food consumption for a period of time. Intermittent fasting involves cycling between periods of fasting and normal eating, and there are several different patterns of fasting. The most common types of fasting include time-restricted eating, circadian rhythm fasting, alternate-day fasting, the 5:2 diet, 5-day fasts, and Eat Stop Eat. 

The potential benefits of intermittent fasting include weight loss, favorable metabolic changes, and healthy longevity. If you plan to try intermittent fasting, make sure to speak with your healthcare provider first.

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